What in your world is deliberately never written down?

Writing usually shows up in worldbuilding as storage. You record a thing so it lasts. What keeps catching my attention in real archives is the other side of that, the material somebody made sure never got in.

In the world I am working on a sealed sentence has legal force, which shifts the question. It stops being what gets recorded and becomes what nobody will put on paper. Prices between two houses stay spoken, because a written price turns into precedent. The order in which the guilds seal at a session is never minuted, since that order is the hierarchy and a minute would make it appealable. Grain quality gets described in words that mean nothing once a court has to read them.

None of that is secrecy in the conspiracy sense. It is people who know exactly what a record does to them.

What stays unwritten in your world on purpose, and who is that gap protecting?